Here at Steve Hoffman forums, I find everything I would of thought fit this category is pretty well remembered..... Outside here even many Beatles songs qualify...
Fleetwood Mac - "Dragonfly" A seemingly 'forgotten' Danny Kirwan-penned B-side that show the band at its most melodic. This is so good that it would have slotted in well on The Pretty Things' 1970 LP Parachute.
Diana Ross - Too Shy To Say Diana Ross covering the Stevie Wonder written album track. It also helps having Richard Perry behind the board. Magic!